PM / devfreq: Add sysfs node to expose available governors

Now that governor list can be variable, knowing the available governors
is useful to be able to select a governor using relevant sysfs node.

Cc: Rajagopal Venkat <rajagopal.venkat@linaro.org>
Cc: MyungJoo Ham <myungjoo.ham@samsung.com>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Kevin Hilman <khilman@ti.com>
Cc: linux-pm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NNishanth Menon <nm@ti.com>
Signed-off-by: NMyungJoo Ham <myungjoo.ham@samsung.com>

Documentation/ABI/testing/sysfs-class-devfreq

@@ -71,3 +71,10 @@ Description:
 		the available frequencies of the corresponding devfreq object.
 		This is a snapshot of available frequencies and not limited
 		by the min/max frequency restrictions.
+
+What:		/sys/class/devfreq/.../available_governors
+Date:		October 2012
+Contact:	Nishanth Menon <nm@ti.com>
+Description:
+		The /sys/class/devfreq/.../available_governors shows
+		currently available governors in the system.

drivers/devfreq/devfreq.c

@@ -730,6 +730,27 @@ static ssize_t store_governor(struct device *dev, struct device_attribute *attr,
 		ret = count;
 	return ret;
 }
+static ssize_t show_available_governors(struct device *d,
+				    struct device_attribute *attr,
+				    char *buf)
+{
+	struct devfreq_governor *tmp_governor;
+	ssize_t count = 0;
+
+	mutex_lock(&devfreq_list_lock);
+	list_for_each_entry(tmp_governor, &devfreq_governor_list, node)
+		count += scnprintf(&buf[count], (PAGE_SIZE - count - 2),
+				   "%s ", tmp_governor->name);
+	mutex_unlock(&devfreq_list_lock);
+
+	/* Truncate the trailing space */
+	if (count)
+		count--;
+
+	count += sprintf(&buf[count], "\n");
+
+	return count;
+}
 
 static ssize_t show_freq(struct device *dev,
 			 struct device_attribute *attr, char *buf)
@@ -917,6 +938,7 @@ static ssize_t show_trans_table(struct device *dev, struct device_attribute *att
 
 static struct device_attribute devfreq_attrs[] = {
 	__ATTR(governor, S_IRUGO | S_IWUSR, show_governor, store_governor),
+	__ATTR(available_governors, S_IRUGO, show_available_governors, NULL),
 	__ATTR(cur_freq, S_IRUGO, show_freq, NULL),
 	__ATTR(available_frequencies, S_IRUGO, show_available_freqs, NULL),
 	__ATTR(target_freq, S_IRUGO, show_target_freq, NULL),